Multiplexing system synchronization



w. H. Buss MULTIFILEXING SYSTEM SYNCHRONIZATION :s sheets-Sheet 1 FiledFeb. l, 1950 ORNEY A INVENTOR Imjf.

nu i nu "VI" VY" July 13, 1954 Filed Feb. l, 1950 W. H. BLISSMULTIPLEXING SYSTEM SYNCHRONIZATION 3 Sheets-Sheet 2 INVENTOR.

Junyv 13, 1954 W H ausg 2,683,768

MULTIPLEXING SYSTEM SYNCHRONIZATION Filed Feb. 1, 1950 3 Sheets-Sheet 3fyi Patented July 13, 1954 ENT FFICE MULTIPLEXING SYSTEM SYNCHRUNIZATIONWarren H. Bliss, Princeton, N. J., assigner to Radio Corporation ofAmerica, a corporation of Delaware Application February 1, 1950, SerialNo. 141,699

16 Claims.

The present invention relates to time multiplex signal transmission andreception methods and apparatus and more particularly, although notnecessarily exclusively, to improvements in time multiplexing methodsand arrangements for transmitting and receiving color televisionsignais.

More directly7 the present invention deals with an improvedsynchronizing method and arrangement for use in time multiplexed colortelevision transmission and receiving systems in which it is required tomaintain a, high degree of synchronous precision between the timemultiplex signal sampling at the transmitter and the time multiplexsignal distribution at the receiver.

rilime division signal multiplexing systems for reducing required signalband width for communications systems are well known in the electricalart. At the transmitter terminal of such a time multiplex system, thereis usually provided some means for sequentially sampling a plurality ofseparate signal intelligence channels to produce a composite signalcomprising a series of grouped pulses, the amplitude variations of anyone pulse of a given group corresponding to signal intelligence derivedfrom a respective signal intelligence channel. At the receiving terminalof the multiplex transmission system there is supplied the counterpartof the signal sampling arrangement at the transmitter. form of a signaldistributing arrangement which receives the series of pulses produced atthe ti nsmitter and distributes these pulses to a plurality of receiversignal channels corresponding in number to the signal intelligencechannels of the transmitter. lt can, therefore, be seen that thesuccessful operation of the transmission and reception system willdepend greatly upon the obtaining of exact isochronism between thetransmitter signal sampling mechanism and the receiver signaldistributing mechanism, for if the transmitter and receiver are not insynchronism in this respect, considerable cross talk in the receiverchannels will result.

More particularly in the time division multiplex system for transmittingand receiving color television images, there are generally provided atthe transmitter three separate component color channels whose outputsare sequentially sampled at a frequency of several megacycles or more.The output of the sampling mechanism is then applied to radiotransmitter for transmission along with the necessary synchronizing andblanking pulses for reproducing the color television image at a remotelocation. The receiver for such a com- This takes the posite colortelevision signal, of course, includes three separate color channelshaving their inputs connected with the output of a signal distributingmechanism. The input of the signal distributing system is suitablysupplied with the received composite signal so that the signal isperiodically dissected and its component pulses properly distributed tothe receiver color channels. As above pointed out, precise isoohronismmust be maintained between the receiver signal distributing mechanismand the transmitter sampling mechanism so that, for example, in a red,green, blue color system, the receiver distributor supplies the receiverred channel with signal information only during the interval in whichthe transmitter sampler is sampling the transmitter red channel.

A more thorough understanding of the importance of multiplexingisochronism between transmitter and receiver terminals of a dotsequential type color television system may be had by reference to twobulletins of Radio Corporation of America, RCA Laboratories Division,respectively entitled Synchronization for Color Dot Interlace in the RCAColor Television System and A l5 x 20" Projection Receiver for the RCAColor Television System, copies of which are filed with the FederalCommunications Commission in Washington, D. C.

Accordingly, it is an object of the present invention to provide animproved synchronizing method and arrangement for maintaining a highdegree of isochronism between a time multiplexing sampling mechanism anda time multiplexing signal distribution mechanism.

A further object of the present invention is to provide an improvedsynchronizing method and arrangement for establishing and maintainingisochronism between the time multiplexing equipments residing inpresent-day dot-sequential color television transmission and receptionequipments.

A further object of the present invention resides in the provision of anew and useful automatic frequency control arrangement for timemultiplex signal distributing equipment which permits the timing ofsignal distribution to be altered in accordance with the character ofinformation distributed by the distributing system.

A still further object of the present invention is involved in animproved method and system for transmitting time multiplexed signalinformation representing a plurality of signal channels such that acomponent of the transmitted signal is indicative of the sequence andtiming of signal channel sampling.

Another object of the present invention is to provide an improved colortelevision transmission and reception method and system of thedot-sequential variety which is characterized by a very high degree ofprecision in color reproduction.

It is a still further object oi the invention to provide an improvementin the overall synchronization system of the color televisionarrangement shown and described in the above-referenced RCA Laboratorybulletins entitled Synchronization of Color Dot Interlace in the RCAColor Television System and A x 20 Projection Receiver for the RCA ColorTelevision System.

In order to realize the above objects and features of advantage, thepresent invention in its more general form as applied to a timemultiplex signal transmitting and receiving system contemplates the useof a signalling system at the transmitting terminal which willperiodically establish the output of the various sampled or commutatedsignal channels, at respective predetermined levels so as to denne, atthe output of the transmitter, a code Waveform of predeterminedcharacter. At the receiving terminal of the multiplex system, theoutputs of at least two of the receiver signal channels to which signalsare fed by the receiver signal distributing system, are compared inamplitude during the transmission of the code Waveform to develop acontrol signal which is indicative of the timing correction necessary inthe phase of the receiver sampler to exact isochronism between it andthe transmitter signal sampling system. This control signal at thereceiver is then applied to a controlling circuit which willappropriately alter the timing of the receiver signal distributingsystem to make any needed correction.

More specically, the present invention as applied to a three colordot-sequential color television transmission and reception systemcontemplates the periodic transmission of a single television image lineor portion thereof, representing a single hue or color, whereby todei-lne at the output of the color television transmitter a codewaveform of predetermined character for the duration of the linetransmission. In general, this single color line or code line isrestricted in its occurrence to the top or bottom of each television eldand is, therefore, synchronously related to the vertical sync pulse ofthe color television transmitter. The color television receiver is thenprovided with a signal sampling mechanism which concomitantly samplesthe output of two of the receiver color channels for an intervalcorresponding to the duration of the single color code line. The outputsof the two channels during the sampled interval are then compared todevelop a control signal which, in turn, is then applied to a controlcircuit which establishes the proper frequency and phase of the colorreceiver time multiplex signal distributing system. The sense of thiscorrection is established so as to maintain precision isochronismbetween the transmitter time multiplex sampling system and the receivertime multiplex signal distributing system.

A more complete understanding of the present invention, as well as otherobjects and features of advantage in addition to those set forthhereinabove, may be obtained through the reading of the followingdescription, especially when v taken in connection with the accompanyingdrawings in which,

Figure l illustrates, by a combination schematic and block diagram, oneform of the present invention finding particular utility in a colortelevision dot-sequential type transmission system;

Figure 2 illustrates by a combination schematic and blockrepresentation, a form of the present invention useful in connectionwith dot sequential color television receivers of a type particularlyadapted to receive the signal produced by the transmitting arrangementof Figure l;

Figure 3 indicates a signal waveform and sampling schedule typical ofthe present invention; and

Figure 4 illustrates another signal waveform and sampling schedulecharacteristic of the present invention.

Turning now to Figure l, the general arrangement here shown, with theexception of the refinements provided by the present inventionhereinafter to be described, represents a color television transmissionsystem of a type described in full detail in the above-referenced RCAbulletin Synchronization for Color Dot Interlace in the RCA ColorTelevision System and appears in Figure 5 thereof. It essentiallycomprises a color camera l0 having red, blue and green output channelsl2, H4 and l5 respectively. The color camera l is synchronized in itsoperation by a master sync generator I8 which in conjunction with aflip-flop oscillator 20 operates to time the three-phase sampling pulsegenerator 22.

vThe sampling pulse generator 22, of course, provides successive keyingpulses separated by 120 degrees for the operation of the red, blue andgreen keyer circuits 2li, 2S and 23, whose outputs are applied forcombining in the added circuit No. 1 at 3i) as described in the abovelaboratory bulletin Synchronization for Color Dot Interlace in the RCAColor Television System. The red, blue and green keyer circuits aresupplied with red, blue and green color channel intelligence signals asprovided by the camera HJ. This is, of course, accomplished through thelow pass filters 32, 34 and 3G intercalated in each of the circuitsextending from the output of the color camera channels and the input ofthe respective color channel keyer. To obtain higher definition effectsin the transmitted picture, the high frequency components of the red,blue and green channels at the output of the color camera i0 arecombined in adder circuit No. 2 at 38 Whose output is filtered by theband pass iilter 40 and also applied to the adder circuit No. 1 at 30.The output of the adder circuit 30 is, of course, communicated by a lowpass filter 42 to a line M indicated for carrying the composite videosignal to a radio transmitter. The elements thus far described operatein exactly the same manner as described in the above-referenced bulletinSynchronization for Color Dot Interlace in the RCA Color TelevisionSystem.

According to the present invention, however, there are placed in thesignal channels existing between the output connections l2, I4 and I5 ofthe color camera I0 and the input of the corresponding low pass lters32, 34 and 35, signal modifying circuits comprising discharge tubes 46,48, 50, 52, 56 and 58. It will be recognized from the circuitrysurrounding discharge tubes 48, 58 and 5S that they act as merelyconventional signal ampliers. Discharge tubes 46, 52 and 58 are alsoarranged as conventional ampliers of the signal-mixing variety such thatsignals may be added to the respective color channels via the controlelectrodes 55, 62 and 64 of these tubes.

In further accord with the present invention, the vertical sync outputof the sync generator it appearing at terminal 56 thereof, is applied tothe input of a delay circuit 58 via capacitor it. The delay circuit 68,comprising discharge tubes 'i2 and 14, is shown, for example, as beingof the typical multivibrator variety having a delay period adjustable bythe variable resistor it. The output of the delay circuit 8 is then.applied Va capacitor 'i8 to another multivibrator circuit 80, comprisingdischarge tubes 82 and 84. This multivibrator circuit 8i) is designatedas a gate control circuit and is adapted to develop a gating pulse 86Whose Width is rendered a function of the setting of the variableresistance 8S of the multivibrator circuit 85. This circuit action isWell known to those skilled in the art and it is not thought to needdetailed description.. Suffice it to say that in one of the preferredforms of operating the present invention, the Width of the pulse 85 byadjustment of resister 823, i

made substantially equal to the period of one television line interval.The inverter circuit Et* receives the gate control pulse 85 and invertsits polarity, as indicated by the Waveform 92, for subsequentapplication via coupling capacitor tl to the mixing grids 68, 52 andiifi of the discharge tubes 4B, 52 and 58 previously described.

Considering novv the operation of the present invention as applied tothe arrangement ci Figure 1, it shall be assumed that the red, blue andgreen color channels l2, i4 and |i are applied to the control electrodes5| and 5l of the discharge tubes 5, 50 and 56 such that a negative swingof these control electrodes Will represent an increase in the brightnessof the respective channel color component. Thus, a decrease in the platecurrent of discharge tube 46 will be evident during intervals in whichthe red component of the transmitted picture increases. Since thedischarge tubes 46, 5t and 56 act as conventional amplifiers, the phaseof the signal applied to the tubes 48, 52 and 553 will, of course, bereversed so that a decrease of the plate current or" tubes 48, 52 and 58Will represent a decrease in the color component represented by therespective color channel. above described, the actuating pulse orcontrol pulse e2 appearing at the output of the inverter circuit 99 isapplied to the control electrodes Si), 62 and Gli of the discharge tubes45, 52 and 5S and with the assumed signal polarity just described, itwill be seen that the negative-going pulse 92 acts in eiect to increasethe brightness of the red color component and decrease the brightness ofthe blue and green color components. In one inode oi the presentinvention, the pulse S2 is made of suliicient amplitude to effectivelysaturate the red channel by driving the tube 46 to cut oi whilevirtually disabling the blue and green channels by driving the tubes 52and 58 to cut off. Hence, for the duration of the actuating pulse 92,the video transmitter, associated with the exemplary embodiment of Fig.l, will transmit only red information and the output of the addercircuit 33 will then comprise a sine .vave it@ substantially as shown inFigure 3. If, as described above, the actuating pulse 92 is made of aduration substantially equal to one line interval, the eiect of thepulse 92 may be viewed as causing the transmitter to transmit a singlered line.

As shown and hereini As pointed out above, it is generally desirable,although not necessarily required, that this single color line producedby the actuating pulse 92 be timed to occur at the top or bottom of avertical picture neld. This removes the likelihood of the single colorline being visible in the picture raster. To achieve this timing, thedelay multivibrator circuit t8, adapted for synchronization by thetrailing edge of the vertical sync pulse derived from the sync separatorI5, may be adjusted by means of resistor 'IE to provide a delay ofsufficient duration that the gate control circuit 8B initiate the frontedge of the gate control pulse te at the beginning of the first scanningline ioliowing the conventional vertical blanking period. Since thedischarge tubes 45, 52 and 58 are driven to cut off by the actuatingpulse it can be seen that the intensity of the red line thus transmittedwill be virtually independent oi other signal information delivered bythe color camera lil. The red signal thus developed may be thought of asa code signal and in conjunction tvith the receiver apparatus about tobe described, may be ingeniously utilized to establish virtually perfectisochronism of the color television receiver signal distributing system.

A receiver arrangement embodying the present invention is shown by Wayof illustration in Fig.

The overall arrangement of the receiver layout in Fig. 2 is, for thepurpose of lending clarity and ease of understanding to the operation ofie present invention, made substantially the same as Fig. l of theabove-referenced RCA Laboratory bulletin A l5 by 20 Projection Receiverfor the RCA Color Television System with, however, the addition of someschematic representations taken from Fig. 9 of the same bulletin.Although suiiciently described in the related text appearing in thebulletin, the operation of the receiver arrangement in Fig. 2, not forthe present considering the novel aspects of the present invention, isbriefly as follows:

A composite multiplexed color television signal produced by thetransmitter arrangement of Fig. l is received by conventional black andwhite receiving circuit |92 via the antenna IM. The compositedemodulated signal appearing at the output terminal |65 of the receiver|62 is then applied to the input of a signal distributing circuitcomprising keyer units |56, |98 and Ili. The synchronizing signalcomponent of the received composite signal is, of course, separated bythe synchronizing signal separator circuit H2 and divided intohorizontal and vertical synchronizing signals made respectivelyavailable to the separator output terminals lid and Ii'. As indicated,these synchronizing signals are utilized in a conventional manner forcontrol of the receiver deilection circuits, as Well as thesynchronization of the receiver signal distributing system.

For this latter purpose of controlling the received multiplexed signaldistributing system, the horizontal synchronizing pulses appearing atterminal H4 are amplified by the discharge tube |48 and applied to adiiferentiating circuit coniprising capacitor |22 and resistance |22taken, of course, in combination with the plate loading resistance |24and plate resistance of the discharge tube |26. As described in theabove-referenced bulletin A 15 x 2G" Projection Receiver for the RCAColor Television System, the differentiated form |27 of the horizontalsynchronizing signal |28 is applied to the control electrode |29 ofdischarge tube |30, Which control 7 electrode is rendered positiverelative to the cathode |32 by merit of its connection throughresistance |22 to a positive power supply potential |34.

To make the correlation of the present systern in Fig. 2 with the Fig. 9of the above-referenced A 15 X 20" Projection Receiver for the RCA ColorTelevision System bulletin more clear, it is noted that the dischargetube |30 of the present Fig. 2 generally corresponds to the dischargetube V4 of the bulletins Fig. 9. Dotted resistance elements |33, |49 and|42 illustrate the connections of the control electrode |20 in themanner indicated in the above-referenced Fig. 9 of the bulletin.

With the control electrode |29 positive with respect to the cathode |32virtually only the negative-gcing peak |44 of the differentiatedhorizontal sync pulse |28 will be passed by the tube |30. In practice,the amplitude of the differentiated sync pulse of the peak |44 is ofsufhcient amplitude to swing the tube 30 well beyond cuto so that acontrol pulse of approximately the form shown at |55 will appear at theoutput of the discharge tube |30. The width of the control pulse |55appearing at the output of the discharge tube |32 may be varied bycontrolling the bias on the control electrode |20. This action obtainsdue to the sloping nature of the back edge |44@ of the differentiatedsync pulse peak |44. The dotted line |26 indicates the point at whichthe grid |29 begins to inuence the plate current of the discharge tube|32 while the dotted line level |52 indicates the signal level at whichthe grid |20 establishes plate current cut off of the tube |32. Thus, byvarying the grid bias on the discharge tube |32, the amount ofdifferentiated sync pulse peak |24, embraced between the levels |56 and|58, may be altered to provide a small variation in the width of thecontrol pulse |55.

As further described in the above RCA Laboratory bulletin A 15 x 20Projection Receiver for the RCA Color Television System, the actuatingpulse |55 is then applied to a three-phase 3.8 mc. sine wave generator150 for synchronization thereof. The sine wave generator synchronizingsystem is such that the generator is disabled for the duration of theactuating pulse |55. The three-phase output of the generator |00 isthen, via circuit paths |62, |54 and |85, applied for control of thekeyer circuits |06, |00 and |90 so that the red, green and blue channelsare `keyed cn during successive discrete signal distributing intervals.Discharge tube ampliers H3, and i l1 corresponding to tubes Vi, V23 andV3| of Fig. 9 in the above-referenced RCA Lab. Bulletin article arerespectively fed by the outputs of the red, green and blue keyers so asto deliver red, green and blue color channel information to the videoamplifiers |10, |12 and |14. As indicated, the output of the videoamplifiers |10, |12 and |14 are respectively fed to color reproducingprojection kinescopes |16. |18 and |80 whose images are opticallycombined by the dichroic mirrors |82 for viewing by the eye at |64.

From the receiver arrangement thus far olescribed, it will be seen thatthe phase of the 3.8 mc. sine wave generator |60 is of prime importancein preventing wrong color information from being distributed to thecolor channels |10, |12 and |14. The sequence of keying the circuits|00, |88 and ||0 must not only agree in frequency to the keyer circuits24, 26 and 28 of the transmitter in Fig. 1 but must occur in exactly thesame sequence and at exactly the same time as the transmitter keyers.The correct phasing of the receiver keyers |06, |08 and |0, as describedin the above-referenced bulletin was accomplished by varying the Widthof the actuating pulse |55 in accordance with the manual potentiometer|40 shown by dotted lines. However, it is easily understood that due toordinary circuitvariations over long operating intervals that frequentadjustment of the width of the actuating pulse |55 would generally haveto be made in order to maintain the exact isochronism between thetransmitter sampling mechanism of Fig. 1 and the receiver signaldistributing system of Fig. 2.

According to the present invention, this phase adjustment isautomatically accomplished by means of the delay circuit |00, gatecontrol circuit |92, and inverter circuit |94 operating to feed a keyingpulse |25 to a two-channel gate circuit comprising discharge tubes |95and. |98. The circuits |20, |92 and |34 of Fig. 2 may, for example, beidentical to the circuits S8, and 00 of Fig. 1 and may be adjusted tooperate in the same manner. The delay circuit is actuated by thevertical sync puise appearing at the output terminal ||S of thesynchronizing signal separator H2. rThus, with the circuits |90, |92 and|94 adjusted in accordance with the corresponding arrangement in Fig. l,the actuating pulse |95 applied tc the common cathode resistance 206 ofthe sampler discharge tubes |95 and |98 in Fig. 2 will be identical tothe actuating pulse 92 of Fig. 1. t will be noted that the commoncathode resistance 200 is through resistance 202 connected with apositive source of potential having a terminal at 20d. It is with suchan arrangement that the discharge tubes |96 and |08 may be staticallybiased at cut off to become conductive only for the duration of thecontrol pulse |05. The grids of the sampler discharge tubes |95 and |98are respectively connected to the output of the blue signal amplier ||1and the green signal amplifier 5. Blue signal pulses will then appear atthe output of discharge tube |96 during conduction thereof and will becoupled via capacitor 200 to the diode 208 having a load resistance 2|0.The polarity with which the diode 263 is connected is such that uponpassing current, the upper terminal of resistance 2|0 will becomepositive with respect to ground. The green signal pulses appearing atthe output of the discharge tube |83 are on the other hand coupled viacapacitor 212 to diode 2|4 connected to pass current through resistance2 it in the opposite direction to the diode 208. Thus, current passingthrough diode 2 |4 will tend to make the upper terminal of theresistance 2|0 negative. Capacitor 2 6 in shunt with resistance 2 |0forms a time constant network of sufficient duration so that successivepulses passed by the diodes 208 and 2|4 from the respective blue andgreen channels may be subtractively combined.

The manner in which the discharge tubes |98 and |93, taken incombination with the diodes 208 and 2|4, act to detect the proper phaseof receiver signal distribution is as follows:

Referring to Fig. 3, there is illustrated the sine wave |02 demodulatedby the receiver |02 during the transmission of the single red line bythe transmitter of Fig. l. The intervals during which the red, green andblue keyers |00, |08 and l0 are successively turned on by the threephase sine wave generator are illustrated at 220, 222, and 224. Asbefore pointed out, when proper absence' synchronization between thereceiver distributor circuit and transmitter is obtained, the reddistribution interval 220 oi the keyer 65 will occur during exactly thesame interval in which the transmitter of Fig. l is sampling the redchan-- nel. Since during the reception of the single color code line,the red channel of Fig. l is turned on to its fullest extent, it followsthat the crest 226 of the sine Wave itil should occur during thereceiver red distribution interval '226. This relationship is shown inFig. 3. Thus, it can be seen that under proper synchronizing conditions,the pulses passed by the green and blue keyer circuits and imrespectively sampling the sine wave Hl@ during intervals 222 and 224will be of equal amplitude and hence will effectively cancel theirstorage eects on capacitor 2 l 5. This means that, under conditions oi'isochronism between receiver and transmitter, the stored effects of thegreen and blue pulses across the capacitor 2l@ will cancel and result ina zero average potential across the capacitor 2 i6. Should, however, thereceiver sine Wave generator Ill advance in phase relative to thereceived sine wave itt, it will be evident that the blue sample takenduring interval 2M will be of greater amplitude than the green sampletaken during interval 222 thereby unbalancing the voltage acrosscapacitor Zit, causing the upper terminal thereof to become positivewith respect to ground. This positive increase in voltage will increasethe plate current of discharge tube i265 operated as a DC amp-liner andcause the grid |29 oi ampliiier tube itil to become slightly morenegative with respect to ground. rlhis Will, in turn, cause the controlpulse 55 to become 0I" less duration and hence correct the timing of thesine Wave generator i6@ in the direction of proper isochronism or thereceiver signal distribution action. On the other hand, should the localreceiver 3.8 mc. oscillator Hit be retarded in phase, a negative voltagewill be produced across the resistor 2li) and the resulting increase inthe width of pulse E55 will cause suitable correction in the sine waveoscillator to produce isochronism.

From the above, it may be seen that the present invention provides anovel automatic synchronizing system for time multiplexed signaldistribution systems and is especially applicable to such systems as areused in color television receivers.

It is Well to note, however, that the present invention in itsapplication to color television receivers oi the type described hereinis in no way limited to the particular color or pulse combinationemployed during the coded line. Furthermore, the duration during which apredetermined amplitude combination. of pulses is transmitted by thecolor transmitter may be more or less than a single image line.

By way of example of another useful pulse and code line combination,there is illustrated in Fig. 4 the operation of the present invention inconnection with a cyan single color line comprising equal amounts oiblue and green. To obtain the transmission of a cyan color line, it willbe necessary merely to reverse the polarity of the actuating pulse 92 ofthe transmitter in Fig. 1 .in its effect on tubes It, 52, and so thatthroughout its duration the red channel will be eiectively disabledwhile the blue and green channels will be given equal increments insignal output. The transmitted video signal will be again sine Wave innature as illustrated by the curve 23@ in Figure 4. Under such.conditions, the red sampling interval 225i will occur during the troughof the sine wave 23@ and the green and blue distribution intervals 222and 224' of the receiver will produce at the respective output of thesample tubes it and R93 pulses ci equal amplitude as in the case of thearrangement of Figure 3. However, it will be seen that the sense oicorrection voltage developed across capacitor 2id will be exactlyopposite from that produced by the arrangement previously described.Here in Figure 4, an advance in the phase o'. the local osc' ator l willcause the blue sampled pulse ring the output of discharge tube l It todecrease instead oi increase, thus making the net voltage shift or theupper terminal of the capacitcr ilt one in the negative directioninstead ci irhe positive direction. To remedy this, it is merelynecessary to reverse the polarity in which the rectiiier units 2% andillfi are connected. Thus, when operating in accordance with thearrangement depicted in -g. diode Z instead of passing current 'throughthe resistor 2li! in a direction so as to malte its upper terminalpositive will be reversed in its connection so that an increase incurrent through the diode 2&3 will cause a negative potential to bedeveloped at the upper end of the resistor.

Other code color lines and pulse combinations useful in the practice ofthe present invention will, of course, occur to those skilled in the artafter having benefited from the above description. Furthermore, theexemplary arrangements of the delay circuit, gate control circuit, andinverter circuit shown in Figures l and 2 may be modified many ways toproduce the desired functions. For example, the inverter circuit @il ofFig. 1, in the case of the alternative arrangement described inconnection with Fig. Al, may be entirely omitted and the pulse et useddirectly for keying or the tubes til, 62, and ell. Moreover, the precisemanner in which the output signals from the sampled receiver channelsduring the period of single color line transmission are compared toproduce a control voltage may be varied to suit individual tastes andconveniences. Correspondingly, the exact mechanism by whichv the phasecontrol voltage thereby developed is employed to shift the phase of thedistributing mechanism control oscillator is of no particularimportance, the arrangement shown in the receiver of Fig. 2 being merelyexemplary of a preferred Way of accomplishing this end.

Having thus described my invention, what I claim is:

1. In a time division multiplexed signal transmission system employing aplurality of signal intelligence sources designated for multiplexedtransmission over a single signal channel to a signal distributionutilization terminal, a synchroniaing signalling arrangement comprisingin combination, an electrical signal sampling mechanism having aplurality of input terminals and at least one output terminal, samplingmechanism being adapted to sequentially and separately channel each ofsaid input terminals to said output terminal at a periodic rate dened bya control signal to form an output terminal signal comprising successivesampled intervals, a source of sampling control signal coupled with saidsampling mechanism for establishing the sampling rate thereof at apredetermined value, coupling means connected between the output of eachof said signal intelligence sources and a respectively differentsampling mechanism input terminal, means for generating an actuatingsignal having a frequency substantially less than said sampling controlsignal but xedly timed relative thereto, signal interrupting meansconnected in series with at least one of said coupling means such as toconditionally suspend intelligence signal iniluence on the correspondingsamplingmechanism input terminal, and signal gating means connected tosaid signal interrupting means for controlling the operation of saidsignal interrupting means in accordance with said actuating signal, saidsignal interrupting means polarized such that the output terminal signalof said sampling mechanism will be indicative of sampling mechanismtiming during the actuation of said interrupting means by said actuatingsignal.

2. Apparatus according to claim 1 wherein means are included for causingsaid interrupting means to be responsive to said actuating signal tointerrupt the intelligence signal for the duration of the waveformcharacteristic of said actuating signal, and wherein said actuatingsignal waveform characteristic duration is made to substantiallycorrespond to an integral number of sampling rate periods.

3. In a time division multiplexed signal transmission system employing aplurality of signal intelligence sources designated for multiplexedtransmission over a single signal channel to a signal distributionutilization terminal, a synchronizing signalling arrangement comprisingin combination, an electrical signal sampling mechanism having aplurality of input terminals and at least one output terminal, saidsampling mechanism being adapted to sequentially and separately channeleach of said input terminals to said output terminal at a periodic ratedefined by a control signal to form an output terminal signal comprisingsuccessive sampled intervals, a source of sampling control signalcoupled with said sampling mechanism for establishing the sampling ratethereof at a predetermined value, coupling means connected between theoutput of each of said signal intelligence sources and a respectivelydiierent sampling mechanism input terminal, means for generating anactuating signal having a frequency substantially less than saidsampling control signal but fixedly timed relative thereto, signaladding means connected in series with at least one of said couplingmeans, electronic control means for applying said actuating signal tosaid signal adding means in such a polarity that the output terminalsignal of said sampling mechanism will be indicative of samplingmechanism timing during the actuation of said interrupting means by saidactuating signal.

4. Apparatus according to claim 3 wherein means are included for causingsaid actuating signal waveform to be of a duration substantially equalto an integral number of sampling rate periods.

5. In a time division multiplexed signal transmission system employing aplurality of signal intelligence sources designated for multiplexedtransmission over a single signal channel to a signal distributionutilization terminal, a synchronizing signalling arrangement comprisingin combination, an electrical signal sampling mechanism having aplurality of input terminals and at least one output terminal, saidsampling mechanism being adapted to sequentially and separately channeleach of said input terminals to said output terminal at a periodic ratedeiined by a control signal to form an output terminal signal comprisingsuccessive sampled intervals, a source of sampling control signalcoupled withsaid sampling mechanism for establishing the sampling ratethereof at a predetermined Value, coupling means connected between theoutput of each of said signal intelligence sources and a respectivelydifferent sampling mechanism input terminal, means for generating anactuating signal having a frequency substantially less than saidsampling control signal but xedly timed relative thereto, signalinterrupting means connected in series with at least one of saidcoupling means such as to conditionally suspend intelligence signalinfluence on the corresponding sampling mechanism input terminal, meansfor timing said signal interrupting means in accordance with saidactuating signal, signal adding means connected in series with at leastone of those coupling means not having a signal interrupting meansconnected in series therewith, means for applying said actuating signalat a constant amplitude to said signal adding means whereby the intervaldefined by the addition of actuating signal information during onesampling interval and the suspension of intelligence signal duringanother sampling interval is indicative of sampling mechanism timing.

6. Apparatus according to claim 5 wherein each of said intelligencesignal sources comprises a. component color channel of a dot-sequentialcolor television system having a predetermined line duration and eldtiming frequency, wherein said interrupting means is responsive to saidactuating signal to interrupt the intelligence signal for the durationof the waveform characteristic of said actuating signal, and whereinsaid actuating signal frequency is equal to said television eld rate andthe active portion of the waveform thereof has a duration substantiallyequal to the duration of a television line.

'7. In a signal receiving system adapted to receive and time distributea composite time division multiplexed signal comprising a synchronizingcomponent and an intelligence component, said intelligence componentcomprising a series of grouped pulses, the individual pulses of eachgroup representing samples of separate respectively commutated signalintelligence sources, certain samples of which have been modified inamplitude to represent the timing of said intelligence sourcecommutation, the frequency of the synchronizing pulse component beingiXedly related to the frequency of the intelligence source commutation,in combination, an electrical signal distributing system having at leastone input terminal and a plurality of output terminals, saiddistributing system being adapted to sequentially and separately channeleach of said output terminals to said input terminal at a periodic ratedefined by a control signal, means for applying received compositesignals to said signal distributing system input terminal, a source ofcontrol signal coupled with said signal distributing system for definingthe distribution timing thereof, means to control the timing of saidcontrol signal source in accordance with a control voltage, means forconcomitantly sampling the signal outputs appearing on at least two ofthe output terminals of said signal distribution system, the timing andduration of said concomitant sampling being in accordance with thetiming and duration of a sampling control signal, means for segregatingsaid composite signal synchronizing component and applying to saidsampling means as a sampling control signal, means for comparing theamplitudes of successive signals alternately sampled by said samplingmeans to develop a control voltage indicative of continuously varyingamplitude differential, and connections for applying said developedcontrol voltage to said distributing system control signal control meansin such electrical sense as to synchronize the timing of said signaldistribution with commutation of said signal intelligence sources.

8. Apparatus according to claim '7 wherein each of the commutatedintelligence sources represented by said composite signal pulsescomprises a color channel of a dot sequential color television systemhaving a predetermined vertical and horizontal synchronizing signalfrequency, and wherein said composite signal synchronizing componentcomprises the vertical synchronizing signal oi said color televisionsystem.

9. A time multiplexed color television transmission system comprising aplurality of color channels connected to the input of a means forsuccessively sampling during sampling intervals of a predeterminedduration and rate of recurrence, the output of each color channel toproduce a series of output pulses, means to develop both verticalhorizontal synchronizing pulses whose recurrence frequenciesrespectively denne the durations of television image raster nd lineintervals, means for generating a con' cl pulse synchronously related tosaid vertical synchronizing pulses, said control pulse having a durationsubstantially greater than the interval between successive samplings ciany given color channel, means intercalated in at least one colorchannel for mixing said control pulse in a signal increasing polaritywith the color signal in channel such that the output of said samplingmechanism will periodically evidence a sustained increase of pulseamplitudes corresponding to the sampling oi said one color channel.

1G. A time multiplexed color television transmission system comprising aplurality of color channels connected to means for successively samplingduring sampling intervals of a predetermined duration and rate ofrecurrence, the output of each color channel to produce a series ofoutput pulses, means to develop both vertical and horizontal.synchronizing pulses whose different recurrcnce frequenciesrespectively define the durations oi television image raster field andline intervals, means for generating a control pulse synchronouslyrelated to said vertical synchronizing pulses, said control pulse havinga duration substantially greater than the interval between successivesamplings of any given color channel, means intercalated in at least twocolor channels for mixing said control pulse in a signal decreasingpolarity with the color signal in said channel, such that the output ofsaid sampling mechanism will periodically evidence a sustained decreaseof pulse amplitudes corresponding to the sampling or" those colorchannels having mixed therewith said control pulse.

11. A time multiplexed color television transmission system comprising aplurality of color channels connected to the input of a mechanism forsuccessively sampling during sampling intervals of a predeterminedduration and rate of recui-rence, the output or each color channel toproduce a series of output pulses, means to develop both vertical andhorizontal synchronizing pulses whose different recurrence frequenciesrespectively denne the durations of television image raster field andline intervals, the combination of, means for generating a control pulsesynchronously related to said vertical synchronizing pulsesy saidcontrol pulse having a duration substantially greater than the intervalbetween successive samplings of any given color channel, and separatemeans intercalated in each color channel for mixing a predeterminedrespective amplitude of said control pulse with the color signal in eachof said channels such that the output of said sampling mechanism willperiodically evidence sustained uniform variations in successive pulseamplitudes indicative of the sequence and timing of signal sampling.

12. A time multiplexed color television transmission system ccmprising aplurality of color channels connected to the input of means forsuccessively sampling during sampling intervals oi a predeterminedduration and rate of recurrence, the output of each color channel toproduce a series of output pulses, said television system includingmeans to develop both vertical and horizontal synchronizing pulses whosediiierent recurrence frequencies respectively denne the durations oftelevision image raster held and line intervals, means for conditionallyconcomitantly establishing the signal amplitude output of each colorchannel at a respective predetermined signal level, means for timing theactuation of said signal establishing means in synchronisrn with saidvertical synchronizing pulse, and means for limiting the duration of theindividual intervals throughout which said signal establishing meansmaintains effect upon being actuated to a period greater than theinterval between successive samplings of any given color channel suchthat the output of said sampling mechanism will periodically evidencesustained uniform variations in successive pulse amplitudes indicativeof the sequence and timing of signal sampling.

13. A color television receiver having a multiplex distributingapparatus, means to time distribute to a plurality of receiver colorchannels a composite color television signal comprising a synchronizingcomponent and an intelligence component, the intelligence component inturn comprising a series of grouped pulses, the amplitude variations ofeach of the separate pulses of a given group nominally representingcolor information for a different color channel, a plurality of saidpulse groups taken together defining information units periodicallyrecurring members of which represent color channel informationcorresponding to but a single color, the recurrence frequency of saidsingle color information units being synchronously related to saidsynchronizing component, an oscillator for generating a control signalcoupled to said distributing apparatus so as to denne the timing ofsignal distribution to said receiver color channels, means forgenerating an actuating pulse in accordance with said receivedsynchronizing component, said actuating pulse having a duration greaterthan the interval between successive distributions to a given colorchannel, means for concomitantly sampling the outputs oi at least two ofsaid receiver color channels for the duration of said actuating pulse,signal amplitude comparing means connected with the output of saidsampling means to develop an output voltage representative of theamplitude dierential between successive pulses from said sampling means,and means for controlling the timing of said oscillator in accordancewith said comparing means output voltage.

14. Apparatus according to claim 13 wherein means are included to causesaid synchronizing component to which said actuating pulse issynchronously related correspond to the vertical synchronizing pulse ofthe color television system and wherein the duration of the actuatingpulse is made substantially equal to one horizontal line interval of thecolor television system.

15. A color television receiver comprising means to receive a compositetime multiplex television signal having a synchronizing component andcolor channel pulse component, a signal distributing apparatus having aninput terminal and a plurality of output terminals to which said inputterminal is periodically and individually coupled in accordance with atiming signal, a separate color channel connected with each distributingapparatus output terminal, a signal generator for developing a timingsignal for said signal distributing apparatus, means for controlling thephase of said timing signal generator in accordance with an actuatingsignal, and means responsive to the output of at least two colorchannels for developing an actuating signal for said control means.

16. Apparatus according to claim 15 wherein said color channel outputresponsive means comprises a signal sampling device adapted to samplesaid color channel outputs at a frequency dened by said synchronizingcomponent.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,037,847 BoWn Apr, 21, 1936 2,418,116 Grieg Api'. l, 19472,465,371 Grieg Mar. 29, 1949 2,521,010 Homrghous Sept. 5, 19502,539,440 Labin Jan. 30, 1951 2,580,G73 Burton Dec, 25, 1951

